EUV light, which is defined as electromagnetic radiation with wavelengths between 124 nm and 10 nm, is used in next-generation photolithography systems to produce structures smaller than is possible with current ultra-violet light sources, such as excimer lasers. One method of generating EUV light is by using a laser to transform a target material, such as xenon or tin, into plasma, which plasma then emits radiation in the EUV portion of electromagnetic spectrum.
One of the difficulties encountered with this type of laser produced plasma EUV light source is the attenuation of the EUV light by amounts of the target material in the path of the EUV light as it leaves the light source. EUV light is strongly absorbed by many substances, including xenon and tin. For example, if the EUV light travels 2 m through xenon at 4 mTorr, which conditions are typical inside extant EUV light sources, approximately 50% of the EUV light will be absorbed by the xenon. This attenuation of the EUV light necessitates generating EUV light at a greater power than is needed for the application, with a corresponding increase in system, operation, and maintenance costs for the EUV light source.
Although the plasma that produces the EUV light is created in a vacuum chamber, which chamber is kept at relatively low pressure by a vacuum pump, injection of target material into the vacuum chamber for plasma generation, movement by currents of buffer gasses, and diffusion results in amounts of the target material throughout the vacuum chamber, including in the EUV light path. Further, some regions of the vacuum chamber may be “stagnation zones” in which target material is not easily removed from the vacuum chamber due to limited interaction with the flows of buffer gas and target material into the vacuum pump.
Thus, what is needed is a system for preventing highly attenuating target material from entering the EUV light path in an EUV light source and for effectively removing the target material from the EUV light source after it is used in the laser produced plasma process.